Gammadoodler
Hero
Even assuming all the fiddly additional modifiers you've added (which are of variable and IMO questionable necessity), at the end of the day you track this maybe..once a level or less, and just enter the result into one place on the character sheet for "base move speed."I see what you're getting at here and in fact like the idea; but once you tack on all the (IMO necessary) modifiers for size, species, and strength/dexterity, tracking everyone's move speed would become - going by the reaction to encumbrance rules, re-rolled initiatives, etc. - more fiddly than a lot of people would seem to want.
And you'd need to do this for all the opponents as well.
This an order of magnitude less fiddly than tracking the weight of every single piece of gear, incremented by items consumed etc.
Heck..it's not significantly more fiddly than what people are already doing (and most of the fiddliness would come from the additional parameters you've added to the equation).
Opponents, like most other creatures would have a statblock, where move speed would just be stated, and you'd use that.
All in all, this seems like an easy thing to implement even with all the things you've added to try and make it difficult.